Environment

Situation

ZEN PXE not
working in a VLAN environment
PXE-e51. No DHCP or BOOTP offers received. Network boot aborted or
terminated.

Resolution

If a
workstation gets the DHCP and PDHCP packets in the same VLAN as the
DHCP and PDHCP server and it doesn't get the packets in another
VLAN, the problem is most likely a switch configuration issue and
not a ZEN configuration issue. Getting a packet trace of all
packets going to and from the workstation from boot up can help
diagnose the issue.

Cabletron
switches DO NOT support two DHCP servers. Move the 'normal' DHCP,
the PXE DHCP and the TFTP services to one server. NT or Netware can
do this.

For a Cisco 3750 48
port switch, try adding the DHCP and PDHCP IP addresses to the
iphelper program in the switch.

Just because a
workstation is getting an IP address from a DHCP server, doesn't
mean that the DHCP packets are coming from the DHCP server. It's
possible that the DHCP packets are coming from DHCP server
software in the switch itself.

Cisco switches
need to have channelling switched off for the DHCP server side.
Channeling is enabled by default. Channelling is a port aggregation
mode where you would have multiple ports attached to the same
device (a server, another switch, etc.) to spread the
load

Try putting
the PDHCP server on a separate server than the DHCP server. Doing
this fixed an issue with a Cisco VLAN switch where IP helper was
enabled to forward client DHCP packets to both the DHCP server and
the PDHCP server.

For a 29xx
series, configuring "SET HOST PORT " will
configure the switch ports for having an edge device
(workstation/printer/server) attached - it shuts off channeling and
enables spantree portfast for the port(s) among other things. Just
remember to set speed and duplex and you should be good to
go.

Try disabling trunking
as a diagnostic measure. It has been known to cause issues with PXE
but the exact reasons are unknown at this time. For more info see
thislink

PortFast has
been known to have been switched off and this has caused issues on
the PXE boot sequence. PXE tends to boot faster and request DHCP
faster than the switch can handle.

PortFast has
been enabled so that the Switch can start talking to a device
without going through the process of waiting for the switch and
device to decide what speed they will communicate, by enabling
Portfast the switch will open the port and enable packets to
flow.

The normal
time period for the Switch to open up a port is around 30 seconds,
with PortFast enabled the clients can start talking as soon as they
are switched on, and in the case of PXE boot services it would not
wait for 30 seconds.

Thedocumentationhas a number of helpful
hints on how to setup PXE in a network
environment.